Fabrication of integrated circuitry typically involves lithographically transferring a pattern which is disposed on a mask onto a layer of material such as photoresist received over a substrate. The pattern on the mask generally defines integrated circuitry patterns and alignment patterns. It has been observed that differences in pattern development of circuit features can depend upon the proximity of the features relative to one another. So-called "proximity effects" in a lithographic process can arise during imaging, resist pattern formation, and subsequent pattern transfer steps such as etching. The magnitude of the proximity effects depends on the proximity or closeness of the two features present on the masking pattern. Proximity effects are known to result from optical diffraction in the projection system used to form the pattern over the substrate. This diffraction causes adjacent features to interact with one another in such a way as to produce pattern-dependent variations. These variations can affect the integrity of the finished devices.
This invention arose out of concerns associated with improving the manner in which integrated circuitry is formed. In particular, this, invention arose out of concerns associated with reducing proximity effects.